The present invention relates to a cathode ray tube for image display and, more particularly, to a cathode ray tube having a voltage-dividing resistor provided in an electron gun housed in its neck portion.
A cathode ray tube for image display has an electron gun for emitting plural electron beams, which electron gun is housed at one end of an evacuated envelope, and a phosphor screen (screen image plane) is formed by coating the internal surface of the other end of the evacuated envelope with a plural-color phosphor layer. Many color cathode ray tubes are also provided with a color selection electrode (for example, a shadow mask) disposed in proximity to the phosphor screen. The main trend in electron guns is a so-called in-line type electron gun which emits three electron beams in parallel with one another in one plane.
FIG. 14 is a perspective view illustrating the construction of a terminal portion of a voltage-dividing resistor 50 of the type installed in an electron gun. FIG. 15 is a partial view illustrating the construction of a terminal portion of this resistor. The voltage-dividing resistor 50 has a resistor layer 22 having a predetermined resistance characteristic, the resistor layer 22 being formed on an insulating substrate 16. An insulating glass coating layer 17 is formed to cover the resistor layer 22 (or resistor pattern). A terminal 53 at one end of the voltage-dividing resistor 50 is connected to a shield cup fixed to a sixth grid electrode, a terminal 51 at the other end of the voltage-dividing resistor 50 is connected to an electrode portion held at a ground potential, and a terminal 52 provided in the middle of the voltage-dividing resistor 50 is connected to an intermediate electrode.
As shown in FIG. 15, the terminal 51 is fixed to the insulating substrate 16 in such a way that a metallic eyelet 511 is caulked to the substrate 16 in the state where the terminal 51 is inserted in a terminal-receiving hole 15, which is a through-hole provided in the substrate 16, and is maintained in contact with a terminal-connecting electrode 14. A connecting portion 51C is formed integrally with the terminal 51.
FIG. 16 is a cross-sectional view of the vicinity of the terminal 51. In the prior art built-in resistor (voltage-dividing resistor), the whole of an electrode-side flange portion 51A is maintained in contact with the terminal-connecting electrode 14 so that the terminal 51 and the terminal-connecting electrode 14 are reliably maintained in contact with each other. In addition, to reliably secure the terminal 51 to the insulating substrate 16, a substrate-side flange portion 51D is constructed so that its edge portion faces outward with respect to the terminal-receiving hole 15. A color cathode ray tube provided with this kind of voltage-dividing resistor is disclosed in, for example, Japanese Utility Model Laid-Open No. 38484/1980.
Built-in resistors for cathode ray tubes of the type which have terminals fixed to an insulating substrate by caulking are disclosed in Japanese Patent Laid-Open Nos. 258680/1993, 68811/1994, 251901/1994, 260119/1997 and 298037/1997.
The metallic eyelet formed of a hard metal material, such as stainless steel, has the problem that it cannot be caulked to a sufficient extent, so that no stable electrical contact is established between the terminal and the conductive layer. To cope with this problem, the load during caulking may be made large. However, if the caulking load is excessively large, the opening edge of the through-hole of the insulating substrate will be damaged. In addition, the related art has the problem that the built-in resistor uses a large number of components and needs a complicated component management and manufacturing process.